Subject: [IPsec] IKEv2: Moving Child SA traffic from an SA to a new SA when rekeying

From: Matthew Cini Sarreo <[email-masked]>
Date: Thu, 16 Apr 2009 18:31:29 +0200

Hello,

When rekeying an IKE SA, the traffic from the old (expiring) SA has to be
moved to the new (rekeyed) SA. How does this go about? Are equivalent Child
SAs created for the rekeyed IKE SA created and the ones in the old IKE SA
deleted (by deleting the IKE SA), or is all data of the Child SA (SPIs, keys
etc) copied as-is to the new SA.

As a visual example:

IKE SA A - Expiring                          IKE SA B - Rekeyed
One Child SA                                   New Child SA
SPI (incoming) 0x12345678               SPI (incoming) 0xABCDEFAB
Protocol AH                                     Protocol AH
                                                       Same cryptographic
suite as A's Child SA

or

IKE SA A - Expiring                          IKE SA B - Rekeyed
One Child SA                                   Copy if Child SA from A
SPI (incoming) 0x12345678               SPI (incoming) 0x12345678
Protocol AH                                     Protocol AH
                                                       Same cryptographic
suite as A's Child SA (copied)

>From section 2.8, "inherits Child SAs" seems to refer to the second case
(copying) but I would like to be 100% sure that this is the case.

Thanks for clarifications.

Regards,
Matthew

---

From: "J. Sun" <[email-masked]>
Date: Thu, 16 Apr 2009 10:43:31 -0700

Matthew,
  It has to be Case #2.  No where in the CREATE_CHILD_SA - IKE_SA Rekey 
exchange do you update to the other endpoint the new CHILD_SA SPIs - 
without exchanging the CHILD_SA SPIs, you'll most definitely run into 
interoperability issues, namely you'll start black holing traffic.  As a 
result, it would be what you consider a copy.  However, you shouldn't 
really think about it in that way.  Depending on implementation, 
generally speaking - CHILD_SAs existing in a SAD would simply have an 
object that essentially references the parenting IKE_SA.  After the 
successful IKE_SA Rekey, the CHILD_SA simply would update this object to 
simply point to its new parent, the rekeyed IKE_SA.  But to qualify, it 
all really depends on implementation.

- Jeff Sun

Matthew Cini Sarreo wrote:
> Hello,
>
> When rekeying an IKE SA, the traffic from the old (expiring) SA has to 
> be moved to the new (rekeyed) SA. How does this go about? Are 
> equivalent Child SAs created for the rekeyed IKE SA created and the 
> ones in the old IKE SA deleted (by deleting the IKE SA), or is all 
> data of the Child SA (SPIs, keys etc) copied as-is to the new SA.
>
> As a visual example:
>
>                                                        Same 
> cryptographic suite as A's Child SA
>
> or
>
>                                                        Same 
> cryptographic suite as A's Child SA (copied)
>
> From section 2.8, "inherits Child SAs" seems to refer to the second 
> case (copying) but I would like to be 100% sure that this is the case.
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> IPsec mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/ipsec
>

---

From: Tero Kivinen <[email-masked]>
Date: Fri, 17 Apr 2009 12:03:03 +0300

> all really depends on implementation.

Actually it is more like of move, not copy, i.e. just like you explain
in the end. There is no two copies of the same Child SA, there is only
one, and that one has exactly one parent SA, i.e. either the old or
new IKE SA, depending on where we are at the IKE SA rekey process.

I.e. it is mostly:

IKE SA A - Expiring                          IKE SA B - Rekeyed
No Child SAs                                 Moved Child SA from A
all Childs are moved to new IKE SA           SPI (incoming) 0x12345678
                                             Protocol AH
                                             Same cryptographic suite
					     as A's Child SA (moved)

I.e. after that you MUST send all management traffic relating the
Child SA using the new IKE SA B, you cannot use IKE SA A anymore for
delete notifications or similar relating to the Child SA which was
moved.

Note, also that in case of the simultaneous rekeys, you need to move
the Child SAs to the winning IKE SA.
-- 
[email-masked]